1. Field of the Invention
This invention relates generally to the field of fluid flow control devices and, more particularly, to valves for switching fluid flows.
2. Description of the Related Art
In semiconductor process apparatuses involving a flow of fluids, there is typically a need to control the magnitude of and path taken by the fluids. For example, there is often a need to switch fluid flows so that at one moment fluid flows from a source along a first path and at another moment fluid flows from the source along a second path.
An example of a process in which fluid flows are switched is oxidation of silicon substrates by pyrogenic steam in a process chamber. The pyrogenic steam is typically formed by combustion of oxygen and hydrogen in a combustion chamber and the steam is then fed from the combustion chamber into the process chamber. A time-consuming procedure, known in the art, is typically followed for the ignition of such a combustion chamber in order to ensure safe operation and to prevent explosions. During the ignition stage, the composition of the gas is not constant and, consequently, is preferably flowed out an exhaust rather than into the process chamber. After its composition has stabilized, the steam can be directed into the process chamber.
In single wafer processing systems in which a series of wafers is processed sequentially one by one, e.g., in wet oxidation systems, it is very time consuming and uneconomical to ignite and then switch-off the combustion chamber for processing each individual wafer. It is more efficient to ignite the combustion chamber at the start of the processing of the series of wafers and to then switch it off when the processing of the entire series is completed.
However, the loading and unloading of an individual wafer of the series of wafers into and out of the processing chamber preferably occurs in inert gas. This inert gas can be provided to the chamber by establishing both a steam flow and an inert gas flow and switching between the flows; for example, in one scenario the steam flow is directed into the processing chamber and the inert gas flow is directed to an exhaust, while in another scenario the steam flow is directed to the exhaust and the inert gas flow is directed into the processing chamber. Switching of the gas flows, however, can easily result in flow and pressure fluctuations, which are undesirable and can negatively affect process results.
In addition, the steam can be quite reactive with metal; this concern is even greater in applications such as semiconductor processing, where corrosive agents such as chlorine are often added to the steam. Because the valves directing the gas flows are typically metallic, these valves can become corroded and the corrosion can lead to contamination of the ultra-pure steam. This corrosion can also detrimentally affect the quality and purity of the process results on the processed substrate.
Consequently, a need exists for a valve that swaps smoothly and rapidly between at least two fluid flows and that is not as susceptible to the issues noted above.